Rubber molding is a molding process that produces a useable rubber product. Rubber products are made from uncured rubber or elastomers. An elastomer is any material with sufficient resilience or memory for returning to its original shape in response to pressure or distortions. Some commonly used examples include hypalon, viton, latex rubber, silicone rubber, nitrile and neoprene. Rubber and elastomers can be derived from natural sources, although they are mostly synthetic, produced through highly controlled chemical processes.

Rubber is an excellent material for situations that require a material to give and return to its original shape. Required information for purchasing rubber molded products includes shape, size and working temperature range. The hardness, which is the amount of resistance to distorting forces, is also an important consideration. Specific industries that benefit from custom molded rubber are automobile, appliance controls, lawn and garden, sporting goods, medical, electrical, government and recreational. These industries and others benefit from the many different products that can be created with this process.

While there are variations in specific methods, all rubber manufacturers use heat and pressure to form molded rubber products. The three most common methods in the rubber molding process are injection molding, compression molding and transfer molding. Each of these is different, but they all involve pouring liquid rubber material into a mold where it is cured in an oven and cooled, thus creating the finished product. Some examples of molded rubber parts include rubber grommets, tubes, shock mounts, stoppers, hoses, bumpers, washers, gasket and seals. Foam rubber goods are also significant due to their many applications.

There are many factors involved in custom rubber molding that affect tolerances. One is shrinkage, where the rubber product reduces in size in the mold after cooling at room temperature. The amount of shrinkage is determined before production and accounted for appropriately in the size of the mold. Another is trimming and finishing, where the excess amounts of rubber that protrude from the mold parting lines are removed. Distortion is an important consideration as well during the molding process, because the shape of rubber is flexible and can be changed according to temperature. For this reason, rubber parts have to be stored at a certain temperature to avoid distortions and thus, ruined products.

Types

Blow molding is a less-common process of placing a hollow tube between the two halves of a blow mold. The blow mold then closes, pinching off the bottom half of the tube, and air is injected into the top, forcing the material outwards to the walls of the blow mold.

Compression molding is a process that compresses the rubber material in a mold under heat and pressure to achieve the desired shape.

Injection molding involves melting rubber in an injection unit and then injecting it into the mold where it stays until after cooling when the finished product is ready.

Transfer molding involves building a "piston and cylinder"-like device in the mold and squirting the rubber into it through small holes. The mold is then closed and under hydraulic pressure the rubber or plastic is forced through a small hole into the cavity where it cures.